Hey there! So cool portrait! I like the facial expression a lot, as well as the flow of your lines :D So. I adjusted the proportions of the face slightly. The eyebrows and eyes were positioned slightly too high, so I moved them downwards. I also reduced the size of the left cheek and ear. I also made the lips slightly wider. Remember that Loomis is a great resource for basic head construction. Reilly's method is also useful for adding rhythm and avoiding "stick" faces. Regarding the shadow: First, you need to establish where the light source is. If you don't establish this, you'll find it difficult to shade the face properly. I position the light source at the top, meaning that any planes not facing upwards will be shaded, such as the eye socket, the bottom of the nose and the sides of the cheeks. I always use Asaro's head as the main source for this, or you can look for references with interesting lighting. The more you observe, the more you'll learn about how light affects the planes of the face. Therefore, you'll eventually be able to shade a head without references. Hope this helps!
